This invention relates generally to camera systems and more particularly to a control system for a cassette-load camera.
There is strong demand in the amateur photography field for camera systems which simplify the task of the operator. Two prime objectives are to free the photographer from unnecessary film handling and from the need to manually adjust the camera exposure setting to the sensitivity of the particular film being used and to the particular light conditions encountered.
The desire to simplify the task of the photographer has led to the development and use of camera systems in which the film is contained within a protective cartridge or cassette, and the camera is specifically adapted to receive the film cassette with a minimum of handling of the film. To enhance simplicity of use, current cassette or cartridge load camera systems also frequently include some form of fully-automatic exposure control system and indicia on the cartridge for automatically adjusting the camera exposure control system to the ASA rating of the film. However, difficulties have been encountered in providing in such a camera a sensitive fully-automatic exposure control system capable of adjustment to a broad range and large number of film sensitivities. The provision of such a broad range film sensitivity adjustment capability has usually required a film sensitivity selector which must be manually set by the photographer and the provision of some form of exposure control on/off switch which must be consciously switched on when the camera is being used and consciously switched off to minimize battery drain by the exposure control system when the camera is not being used. It is the principal object of the present invention to provide a control system for a cassette-load camera which overcomes these difficulties.
Briefly described, the present invention provides a cassette-load camera control system for adjusting the exposure control system of the camera to the sensitivity of the film contained in the cassette comprising variable neutral density filter means positioned in optical alignment with the exposure control system light sensing photocell for selectively altering the quantity of light incident upon the photocell, filter setting means responsive to indicia provided on the film cassette to effect a particular neutral density setting for the variable density filter means related to the sensitivity of the film in the film cassette, sensitivity range control means for adjusting the camera exposure control system alternatively for a range of high film sensitivities or a range of low film sensitivities, and range setting means responsive to other indicia provided on the film cassette to effect setting of the range control means to either the high film-sensitivity range or the low film-sensitivity range as related to the sensitivity of the film contained in the film cassette. The filter setting means aand the range setting means are correlated to effect adjustment of the camera exposure control system to the particular sensitivity of the film contained in the film cassette.
The range switching means preferably comprises a resistance network for establishing a reference level for the photocell and switch means responsive to the range setting means for switching said resistance network alternatively between a first reference level setting for a high film-sensitivity range and a second reference level for a low film-sensitivity range.
To achieve requisite level of sensitivity, the camera exposure control system preferably employs a photo-resistive-type photocell which requires a source of electrical energy for operation. In a cassette-load movie camera, a common source of electrical power is provided to provide energy for both the exposure control system and the film and shutter drive motor. To control energization of the exposure control system relative to energization of the motor drive system in such a camera, the control system of the present invention further comprises a camera control grip including a master control switch means normally biased to an open condition and adapted in closed condition to collect the camera exposure control system to the power source and a motor control switch means normally biased to an open condition and adapted in closed condition to connect the power source to the drive motor. The master control switch means and the motor control switch means are arranged so that normal manual grasping of the grip closes the master control switch means before the motor control switch means can be closed so that the exposure control system is energized before energization of the drive motor. An electrical circuit is arranged to connect the power source to the drive motor and the exposure control system and is effective to render the motor control switch inoperative to energize the drive motor until the master control switch means is closed.